Metallic carbides and a process of producing the same



Se t. 3, 1968 R. a. BOURDEAU 3,399,980

METALLIC CARBIDES AND A PROCESS OF PRODUCING THE SAME Filed Dec. 28, 1965 2 Sheets-Sheet 1 INVENTOR. ROMEO G. BOURDEAU MJWMM A TTORNEV [IMQT 76 Known Hm! Sept. 3, 1968 R. s. BOURDEAU METALLIC CARBIDES AND A PROCESS OF PRODUCING THE SAME Filed Dec. 28, 1965 2 Sheets-Sheet 2 Ill INVENTOR. ROMEO G. BOURDEAU Br be A TTORNEY United States Patent 3,399,980 METALLIC CARBHDES AND A PROCESS OF PRODUCING THE SAME Romeo G. Bonrtleau, Wapping, Conn., assignor, by mesne assignments, to Union Carbide Corporation, a corporation of New York Continuation-impart of application Ser. No. 172,973, Feb. 13, 1962. This application Dec. 28, 1965, Ser. No. 516,928

Claims. (Cl. 23-345) This application is a continuation-in-part of application Ser. No. 172,973, entitled Metallic Carbides And A Process Of Producin The Same, filed Feb. 13, 1962, now abandoned.

The present invention relates to metallic carbides and particularly to an improved process for use in producing metallic carbides.

Today, the utilization of extremely high temperatures is becoming a normal processing technique. A need, therefore, has arisen for materials which will withstand temperatures in excess of 6000 F. Materials which have been considered quite effective for this purpose include the carbides of tantalum, hafnium, niobium, titanium, silicon, zirconium, tungsten, molybdenum, thorium and uranium.

The use of these carbides, however, is somewhat curtailed because they are not conveniently produced in a relatively pure state. For instance, these carbides are produced by the reaction of a metallic halide, a hydrocarbon and hydrogen at a substantially high temperature. This process, however, is rather difiicult to control if carried out on a large scale. The difficulty is due to the fact that large quantities of hydrogen are extremely dangerous to handle especially at the temperatures required for the reaction to effectively produce the metallic carbides. Another disadvantage is that the hydrogen required in the process accelerates the decomposition of the metallic halide to the corresponding free metal. The product which is, therefore, obtained is always contaminated by the free metal and this, in turn, adversely affects the physical properties of the final product.

An object of this invention is to provide a process for producing metallic carbides which does not necessitate the use of hydrogen as a reactant.

Another object of this invention is a process which may be used to produce a metallic carbide in a relatively pure state.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

We have discovered that a metallic carbide tantalum carbide, hafnium carbide, niobium titanium carbide, silicon carbide, zirconium carbide, tungsten carbide, molybdenum carbide, thorium carbide, or uranium carbide may be produced under certain conditions by the gaseous reaction of the corresponding metallic halide with an ordinary hydrocarbon such as rnethane. In the case of tantalum carbide, the overall reaction may be illustrated as follows:

such as carbide,

heat (1) Ta Cls 'Ia 2% C12 heat (2) CH1 0 2H:

(3) Ta o Ta 0 As is apparent from the foregoing, although hydrogen gas may be liberated it is not utilized as a reactant in the system. The reaction, therefore, may be successfully utilized without any of the necessary precautions which usually attend the use of hydrogen. This advantage re- 3,399,989 Patented Sept. 3, 1968 ice sults in a process which is cheaper and much more convenient to carry out on a commercial scale than the prior process heretofore described. Another advantage lies in the fact that the metallic carbide produced by the process of this invention is relatively pure, i.e., it is not contaminated with the corresponding free metal. The product, as a result, has been found to exhibit improved characteristics, such as hardness, which will be more fully described at a later point in this specification.

Broadly the process of this invention is used to produce a metallic carbide by reacting the vapors of a metallic chloride such as tantalum chloride, hafnium chloride, or niobium chloride, with a gaseous hydrocarbon such as methane within the temperature range of 1500 C. to 3000 C. and the pressure range of 1 mm. to 200 mm. of mercury.

One aspect of this invention is a process which is used to produce a metallic carbide powder by reacting the vapors of a metallic chloride selected from the group consisting of tantalum chloride, hafnium chloride, niobium chloride, titanium chloride, silicon chloride, zirconium chloride, tungsten chloride, molybdenum chloride, thorium chloride, and uranium chloride with a gaseous hydrocarbon within the temperature range of 1500 C. to 3000 C. and the pressure range of 10 mm. to 200 mm. of mercury.

Another aspect of this invention is a process which is used to produce a metallic carbide of superior hardness by reacting the vapors of a metallic halide such as tantalum chloride, hafnium chloride, niobium chloride, titanium chloride, silicon chloride, zirconium chloride, tungsten chloride, molybdenum chloride, thorium chloride, and uranium chloride with a gaseous hydrocarbon within the temperature range of 1500 C. to 3000 C. and a pressure range of 1 mm. to mm. of mercury.

A further aspect of this invention is a process which may be used to coat a suitable substrate with a metallic carbide by contacting the surface of the substrate with the vapors of a hydrocarbon gas and a metallic halide selected from the group consisting of a tantalum halide, hafnium halide, niobium halide, titanium halide, silicon halide, zirconium halide, tungsten halide, molybdenum halide, thorium halide, and uranium halide within the temperature range between 1700 C. and 2500 C. and a p essure range between 1 mm. and 100 mm. of mercur These processes in general utilize a vapor-phase technique in which the carbide of either tantalum, hafnium, niobium, titanium, silicon, zirconium, tungsten, molybdenum, thorium, or uranium is deposited onto a heated surface by the thermal decomposition and inter-reaction of the appropriate metallic halide and a hydrocarbon gas. The various techniques utilized in each of the processes are described in detail as follows:

FIGURE 1 is a front view in section of the apparatus within which the present processes may be carried out.

FIGURE 2 is a front view in section of a novel unit which may be used to convey the heated reactants to the deposition zone of a furnace.

FIGURE 3 is a diagrammatic view of a metallic halide feed mechanism which may be used in conjunction with the evaporating system.

FIGURE 4 is a diagrammatic view of a metallic halide generator for use with the evaporating system.

In general, a powdered metallic halide is added to the evaporator 12 through inlet 13. The evaporator 12 is provided with an exhaust line 14 which, in turn, is adapted with a suitable heating means 15 and a conventional flowmeter 16-. The temperature of the evaporator 12 is then raised by means of a suitable heating jacket 17. The temperature of the evaporator is set at a point above the melting point of the particular metallic halide used in the system. This will usually be between about 100 C. and 300 C. The rate of flow of the vapors of metallic halide travelling through the exhaust line 14 to the feed line 18 is controlled by valve 19. Simultaneously, a hydrocarbon gas such as methane is introduced into feed line 21 which is also adapted with a suitable heating means. The temperature of the hydrocarbon gas travelling feed line 21 is maintained within the range of 100 C. to 300 C. The rate of fiow of the reactant gases should be such as to provide a carbon to metal ratio of 0.1 to 20; the preferred ratio being 2.

The two gases travelling through their separate feed lines 18 and 21 meet at junction 22 and are directed through central feed line 23 which is also adapted with a suitable heating means. The gases are substantially mixed in their travel through feed line 23 and are introduced in this state to an improved injector 24, as previously stated, the molar ratio of carbon to metal being 0.1 to 20. These reactants pass through the injector to the hottest point of the furnace, at which point they react producing a metallic carbide compound which will deposit itself on any surface that is present.

The improved injector 24, as shown in FIGURE 2, consists of a plurality of cylindrical hollow tubes each of which is in coaxial relationship to the other. The innermost or base tube 27, which is of open-end construction, is preferably made of stainless steel. A substantial portion of the base tube 27, i.e. the body portion and lower portion, is covered with a ceramic coating 28 which functions as a housing within which a heating element is embedded. The heating element, as

shown, may be resistance wire 29. The upper end of the uncoated portion of the tube 27 is adapted to be connected to a central feed-line 23. In this manner, the commingled vapors of each of the reactants are fed into the hot injector 24. The tube 31 adjacent the outer surface of the base tube 27 functions as an insulation jacket and the air-space circumscribed by tube 31 serves as an insulation zone. The outermost tube 32 and tube 33 which lies adjacent the inner surface thereof function together in combination as a water jacket. The upper end of the outermost tube 32 is provided with an inlet fitting 34 which communicates with the space 35 existing between the inner surface of tube 32 and the outer surface of tube 33. The upper end of tube 33 is provided with an exhaust fitting 36 which communicates with the space 37 existing between the inner surface of tube 33 and the outer surface of the insulation jacket 31. Space 35 communicates with space 37 at the lower end of tube 33. Space 35 functions as an inlet passage for the particular coolant used in the system, while space 37 functions as an exhaust passage for the same coolant. Water is the coolant usually utilized in the system and this enters inlet passage 35 through inlet fitting 34, passes through exhaust passage 37, and leaves the jacket through fitting 36. The lower end of tube 27, insulation jacket 31, and the outermost tube 32 are joined by means of a common weld 38.

This novel injector is used to transport the vaporous reactants from the central feed line 23 to the deposition zone of the furnace. It has been found that the metallic halide, in many cases, must be maintained at an elevated temperature during transport because otherwise the halide would condense, form a solid, and thereby plug the feed lines of the system. As heretofore described, the base tube 27 is provided with an insulation jacket 31 which aids in maintaining the temperature within the base tube. This prevents any major fluctuation in the temperature of the vapors as they pass through tube 27. The combination water jacket which circumscribes the injector 24 functions to prevent damage or deterioration to the gasket ring 39 provided on flange 41 during the heating stage of the process. Gasket ring 39 is designed to circumscribe the outer surface of the novel injector and to hold the injector in position when the same is inserted in the furnace. Due to the fact that the injector is water cooled, it may be directly introduced into the hot zone of the furnace without adversely affecting the temperature in the base tube. Therefore, the vaporous reactants will not prematurely react with each other while passing through the injector. This aids in producing a clean-cut deposition in the deposition tube 42 of the furnace.

The injector, when suitably mounted, will fit into the conventional furnace 43 which is commonly used for vapor-phase depositions as shown in FIGURE 1. A suitable substrate, such as graphite, 44 should be mounted in deposition tube 42 if it is desired to produce a coating by this process. However, if it is desired to produce the metallic carbide as a powder, a substrate should not be mounted in the deposition tube 42. In this case, the vaporous reactants are introduced into the deposition zone of the furnace at which time the metallic carbide will deposit itself on the Wall of the deposition tube 42. After a suitable time, the system may be shut down and the metallic carbide may be scraped from the walls in the form of a powder.

The hydrocarbon gas or gases which may be used in this process include any carbon based gas capable of producing a carbonaceous deposit when subjected to a suitable decomposition temperature. For illustrative purposes, the hydrocarbon gas may be either methane, ethane, propane or benzene.

The present process is operative within the temperature range of about 1500 C. to 3000* C. If the process is carried out at a temperature below 1500 C., the decomposition rate will be exceedingly small and the process would be impractical for commercial purposes. The decomposition rate will vary from between 0.1 and 50 mils per hour depending on the flow rate used and the area of the deposition surface. It would also be impractical to operate the process above 3000 C. because the end-product, i.e., the metallic carbide, will substantially decompose above this temperature. As heretofore described, this process may be utilized to produce a coating or a powder depending on the particular technique utilized. It has been found that the present process will operatively produce a metallic carbide within the range set forth above, but it is preferred to have the temperature somewhere between about 2000 C. and 3000* C. if it is desired to produce a metallic carbide having a superior hardness. However, if it is desired to coat a substrate, the temperature of the process should preferably be within the range of 1700* to 2500 C. It has been found that the process is highly effective within the latter range, especially around a temperature of 2000 C., and that the coatings produced within this range possess a high degree of strength and a high density. Whenever the expression deposition temperature is used in the specification or claims, it is intended to mean the temperature at which the gases will decompose and react with each other to effect a deposit of metallic carbide upon a suitable exposed surface.

The pressure of the process is inter-related with temperature which has been discussed above. This process is operative within the pressure range of about 1 mm. to 200 mm. of mercury. The specific pressures utilized within this range will depend on the product desired i.e. whether the metallic carbide is to be a coating, a powder, or a metallic carbide of superior hardness. If it is desired to produce a coating, the pressure should be preferably within the range of 1 mm. to mm. of mercury. A variation in pressure will somewhat affect the disposition rate of the coating. If the pressure of the coating process is maintained below 1 mm. of mercury, the rate of deposition of the coating will be reduced. However, if the pressure is allowed to increase above 200 mm. of mercury, the deposit will consist primarily of soot. In any case, as the pressure is increased, the reaction rate will increase until a limiting pressure is reached and soot begins to form. If it is desired to produce a metallic carbide having a superior hardness, the pressure should be within the range of 1 mm. to 20 mm. of mercury. However, if it is desired to produce a powder by the technique heretofore described, the presure is preferably maintained within the range of 100 mm. to 200 mm. of mercury. In any case, however, the process will operatively produce a metallic carbide if the pressure is between 1 mm. and 200 mm. of mercury.

The following examples will illustrate the process. Example 1, for instance, sets forth the conditions under 6 carbide having a melting point of 6330 F. as well as other carbides as heretofore mentioned.

Example 3, which follows, sets forth the conditions under which a metallic carbide having superior hardness is produced.

EXAMPLE 3 The temperature of the furnace was brought within the range of 2000 C. to 3000 C. and the pressure was maintained between 1 and 20 mm. of mercury. The total which the metallic carbide was produced as a powder. 10 flow fate of the reactants, tantalum Pefltflchlofide and methane gas, entering the deposition zone of the EXAMPLE 1 furnace was about 1 liter per minute. After a suitable The temperature of the furnace was brought to 2100 C. time, the temperature and pressure were allowed to reand the pressure was maintained between 100 to 200 mm. turn to normal and the product was removed from the of mercury. Tantalum pentachloride and methane were furnace. introduced into the system such that the total flow rate The hardness of the product was determined by means of the vaporous reactants passing through the injector 0f a Kentron microhardness tester. This unit employs a into the deposition zone of the furnace was maintained diamond tipped indenter which makes an impression on at about 1 liter per minute. After a suitable time, the 20 the surface of the material being tested. The impression temperature and pressure was allowed to return to normal was made under a constant load of 100 grams. The area and the product was scraped from the deposition tube of impression is calculated by determining the size thereof of the furnace in the form of a powder. and the value obtained is expressed in kilograms per Various conditions under which similar experiments square millimeter which stands for the microhardness of were carried out are set forth in Table I which follows: the material being tested.

Table III indicates some of values (A) obtained on TABLE I products produced by the present process and they are Pressure, mm. Temperature, 0. Flow Rate, liter compared to values (B) obtained on products produced per mmute by the prior art process heretofore described. g: i TABLE III 31008 1 A B TaO 2,160 to 5,490 1,800 to 1,952. In all cases the particle size of the powder obtained g 3 288 :8 5 888 21400) 2,470- was in the order of 1 micron. Other powdered carbides which may be produced by this techmque include m b Table I indicates that a product produced by the preshathtum h a tltahtum h 5111mm ent process is quite superior in hardness to products prohlde: Zlrcohlhm h and h cathldes of tungsten: duced by the conventional process. This is because the motyhdehuth, thonum and t These Powders may product produced by the present process contains a greater be molded 111th y Shape that 15 deslred- 4O amount of carbon. During normal processing, the metal EXEIIIPI? which follows, P forth the cohdltlohs and carbon atoms are deposited together. When an atuhdQY Whtch the metalhc carbide was Produced as a mosphere rich in carbon is used, a carbide rich in carbon coatmg- I is produced. At high temperatures, the distance between EXAMPLE 2 the metal atoms is increased because of the higher mode A suitable Substrate was mounted i the d i i of vibration and it is possible to introduce more carbon tube f a f r The temperature f h f r a was mto the lattice. The result is a carbide having a distorted brought to 2000 d the Pressure was i i d lattice and one that is consequently harder. Carbides probetween 1 mm. and 200 mm. of mercury. Tantalum pentaduced F these high ttiInPerattlrtfls have hamdnesses pchloride and methane were then introduced into the sys- Proachmg f f and y replace diamonds in 1111mtem. The total flow rate of the gaseous reactants entering her t apphcatlons ifistaflc? a Pollshing agent, a the deposition zone of the furnace was about 1 liter per toot h mammal f all abrasive grindiflg Wheels- In minute. After a suitable time, the temperature and prestact, some aPPhCatIOIIS, t metallic Cafbldes Produced sure were allowed to return to normal and the coated by this Process SUPEHOT t0 diamonds because the substrate was removed from the fumacez The Surface f metallic carbide will not break down at high temperatures the substrate was very hard and extremely corrosive reas olldlnal'y dlamonds h b sistant. The melting point of the coating was found to Table IV sets forth conditions under WhlCh smnlar be about 70200 Q metalllc carbides have been produced. In each case, the

Similar coatings were produced even though the com carb1de produced exh1b1ted a superior hardness. ditions under which the experiment was performed varied TABLE IV as follows: Pressure, mm. Temperature, 0. Flow Rate, liter per TABLE II minute Pressure, mm. Temperature, 0. Flow Rate, liter 3' i per minute 000 1 gggg S: 888 l 1; 700 1 3,000 1 2,500 1 The carbide in each of these cases is formed by a reduction or diffusion process wherein the metal is made to accept carbon atoms interstitially into its lattice. The available space in the metal is limited so only a certain number of carbon atoms can be introduced. Other coatings which may be produced by this method include hafnium carbide having a melting point of 7030 F. and niobium FIGURE 3 illustrates another embodiment of a metal halide metering system which may be used in place of the above described metering system as illustrated in FIGURE 1. t

The metering system 4-9 of FIGURE 3 comprises a hopper 59 adapted to hold a metal halide powder 51. The powder 51 is dispensed downwardly into a suitable evaporation section 52 by means of a feed gear 53 driven by a variable speed motor 54. The feeding of the powder 51 is facilitated by a vibrator 55 mounted adjacent to the feed gear 53, and also by the injection of a neutral gas of methane by inlet 57 into hopper 50 and into the discharge inlet 56 beneath the feed gear 53. A heater suitable coil 58 is provided around the evaporator section 52. The evaporator section outlet 59 is coupled to the injector in a manner similar to the above described metering system of FIGURE 1.

FIGURE 4 illustrates another embodiment of a metering system 60 adapted for use with a finely divided metal charge 61 and is used for a complete conversion from the metal charge 61 such as niobium, tantalum, hafnium, titanium, silicon, zirconium, tungsten, molybdenum, thorium and uranium. The finely divided metal charge 61 is placed in an enclosed container 62 surrounded by a heater 63 capable of heating the material at temperatures between 200 and 700 C. Chlorine is fed through an inlet 64 and downwardly through the metal charge 61 causing a metal halide to fiow from the outlet 65 to an injector as described above.

There are many advantages inherent in the present process other than those heretofore set forth. These are all intended to be covered by the scope of this invention. As various changes may be made in the form, apparatus, and conditions of the process herein described without departing from the spirit and scope of the invention, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process wherein a metallic carbide is produced which comprises inter-reacting a hydrocarbon gas With a metallic halide within a temperature range of 1500 C. to 3000 C. and a pressure range of 1 to 200 mm. of mercury, said metallic halide being selected from the group consisting of the halides of the metals selected from the group consisting of tantalum, hafnium, niobium, titanium, zirconium, silicon, tungsten, molybdenum, thorium and uranium, the ratio of hydrocarbon gas to metallic halide being such as to provide a carbon to metal molar ratio of 0.1 to 20.

2. The process as in claim 1 wherein the metallic halide employed is a metallic chloride, the temperature 8 employed is 1700 C. to 2500 C., and the metallic carbide is deposited as a coating or a substrate.

3. The process as in claim 2 wherein the temperature employed is about 2000 C.

4. The process as in claim 1 wherein the metallic halide employed is a metallic chloride, the pressure employed is 100 to 200 mm. of mercury, and the metallic carbide is produced in the form of a powder.

5. The process as in claim 1 wherein the metallic halide employed is a metallic chloride, the temperature employed is 2000 C. to 3000 C., the pressure employed is 1 to 100 mm. of mercury, and the metallic carbide produced is of superior hardness.

References Cited UNITED STATES PATENTS 1,987,576 1/1935 Moers 117-231 2,580,349 12/ 1951 Fisher 23-349 2,962,388 11/1960 Ruppert 23-208 X 2,978,358 4/1961 Campbell 23--208 X 3,001,238 9/1961 Goeddel 23-208 X 3,046,090 7/1962 Powers 23349 3,085,863 4/1963 Prener 23208 3,205,042 9/1965 Jacobson 73208 FOREIGN PATENTS 1,088,863 9/1960 Germany.

778,267 7/1957 Great Britain.

OTHER REFERENCES I. E. Campbell, The Vapor Phase Deposition of Refractory Materials, Trans. of Electrochemical Society (November 1949), pp. 318, 319, 322, 323.

D. M. Helton, A Preliminary Study on Uranium Carbide Synthesis Using a Plasma Jet, ORNL-TM-872;

Kendall, Preparation of Pure SiC, vol. 1, pp. 171- 173, International Congress of Pure and Applied Chemistry, 1947.

CARL D. QUARFORTH, Primaiy Examiner.

A. J. STEINER, Assistant Examiner. 

1. THE PROCESS WHEREIN A METALLIC CARBIDE IS PRODUCED WHICH COMPRISES INTER-REACTING A HYDROCARBON GAS WITH A METALLIC HALIDE WITHIN A TEMPERATURE RANGE OF 1500*C. TO 3000*C. AND A PRESSURE RANGE OF 1 TO 200 MM. OF MERCURY, SAID METALLIC HALIDE BEING SELECTED FROM THE GROUP CONSISTING OF THE HALIDES OF THE METALS SELECTED FROM THE GROUP CONSISTING OF TANTALUM, HAFNIUM, NIOBIUM, TITANIUM, ZIRCONIUM, SILICON, TUNGSTEN, MOLYBDENUM, THORIUM AND URANIUM, THE RATIO OF HYDROCARBON GAS TO METALLIC HALIDE BEING SUCH AS TO PROVIDE A CARBON TO METAL MOLAR RATIO OF 0.1 TO
 20. 